Machine for converting thermal energy into electrical energy or vice versa

Abstract

A machine for converting thermal energy originating from waste heat deposits into electrical energy. It uses the magnetic phase transition properties of certain materials when they are exposed to a temperature variation with respect to their Curie temperature. The machine includes a magnetothermal converter provided with a fixed stator provided with active elements made of the materials, and a mobile rotor provided with magnetic poles and non-magnetic poles. The machine includes a closed fluidic circuit of heat-transfer fluid, coupled with two thermal sources of different temperatures by means of heat exchangers and with the stator to transfer thermal energy collected in the active elements. A synchronization system makes it possible to expose the active elements to alternating thermal cycles to generate a permanent magnetic imbalance between the rotor and the stator, and generate a displacement of the rotor, creating mechanical energy that can be converted into electrical energy.

The invention claimed is: 
     
       1. A conversion machine for converting thermal energy into electrical energy, or conversely, electrical energy into thermal energy, said conversion machine comprising at least one magnetothermal converter arranged to convert a temperature variation into mechanical energy or a magnetic field variation into thermal energy, said magnetothermal converter comprising active elements with magnetic or thermal phase transition, and a thermal or magnetic modulation unit arranged to expose said active elements to a temperature variation or to a magnetic field variation having for effect to respectively vary the magnetic state of said active elements or the temperature of said active elements, and at least one closed circuit inside said magnetothermal converter, wherein a heat-transfer fluid circulates in a closed circuit through said active elements and at least one heat exchanger, arranged to thermally couple said active elements with at least one external device by means of said at least one heat exchanger, said magnetothermal converter comprising a fixed stator provided with said active elements, said active elements being distributed in said stator into a first group of active elements in a first magnetic or thermal state, and into a second group of active elements in a second magnetic or thermal state different from said first magnetic or thermal state, the active elements of the first group being alternated with the active elements of the second group so as to create an alternation between active elements in said first magnetic or thermal state and active elements in said second magnetic or thermal state, and said magnetothermal converter further comprising at least one mobile rotor shifting or rotating in relation to said stator, said rotor being equally provided with magnetic poles and non-magnetic poles alternated and regularly distributed, such that they each extend over an angular sector of the same value, the alternating arrangement of the magnetic poles and the non-magnetic poles corresponding to the alternating arrangement of the active elements of said first group and active elements of said second group, such that when an active element of said first group faces a magnetic pole, an active element of said second group faces a non-magnetic pole, and vice versa. 
     
     
       2. A conversion machine according to  claim 1 , wherein said magnetothermal converter comprises a fixed magnetic frame superimposed on said rotor to delimit between them an air gap wherein is arranged said stator, said magnetic frame being arranged to channel the magnetic flow and close the field lines of the magnetic poles of said rotor through said stator and said active elements. 
     
     
       3. A conversion machine according to  claim 1 , wherein said magnetothermal converter comprises two rotors superimposed to delimit between them an air gap wherein said stator is arranged, the two rotors having the same number of magnetic and non-magnetic poles, and being arranged to channel the magnetic flow and close the field lines of the magnetic poles of the two rotors through said stator and said active elements, and wherein the two rotors are coupled together by mechanical connection or by magnetic coupling. 
     
     
       4. A conversion machine according to  claim 1 , wherein said stator comprises or forms a thermally insulating support, on which are fixed said active elements, as well as fluidic connections to allow said fluidic circuit to communicate with said active elements, and wherein said active elements are distributed over said stator and separated from each other by a pitch preferably regular and as small as possible to maximize the quantity of active elements in said stator. 
     
     
       5. A conversion machine according to  claim 1 , wherein said stator comprises a number of active elements which is a multiple of the number of magnetic and non-magnetic poles of said at least one rotor. 
     
     
       6. A conversion machine according to  claim 1 , wherein said fluidic circuit comprises said heat-transfer fluid selected from the group comprising an aqueous solution with or without additive, a gaseous medium, a liquefied gas, a petroleum product, and wherein said active elements comprise fluidic passages to allow said heat-transfer fluid to circulate through said active elements. 
     
     
       7. A conversion machine according to  claim 1 , wherein said fluidic circuit comprises a pump, two heat exchangers and two circulation loops for said heat-transfer fluid connected in parallel by a synchronization system, and wherein said synchronization system is arranged to connect said active elements respectively from said first group and from said second group in series with said heat exchangers alternately in one and the other of said circulation loops and creating an alternation of thermal or magnetocaloric cycles at a determined switching frequency. 
     
     
       8. A conversion machine according to  claim 7 , wherein said synchronization system comprises fluidic distributors controlled according to said determined switching frequency by an actuator selected from mechanical, hydraulic, electric and/or electronic actuators, and arranged to circulate said heat-transfer fluid alternately in said active elements in one direction in said first circulation loop, and in the opposite direction in said second circulation loop. 
     
     
       9. A conversion machine according to  claim 8 , wherein said fluidic distributors are controlled by said at least one rotor of the magnetothermal converter and a mechanical cam transmission by a variable-speed auxiliary motor and a mechanical cam transmission, or by a programmable electric or electronic cam. 
     
     
       10. A conversion machine according to  claim 7 , wherein the said fluidic circuit comprises a buffer tank of heat-transfer fluid connected in series with each of the said circulation loops. 
     
     
       11. A conversion machine according to  claim 7 , wherein the said fluidic circuit further comprises control units for the direction of circulation of said heat-transfer fluid arranged to make the heat-transfer fluid circulate in each of the said heat exchangers in a single direction of circulation. 
     
     
       12. A conversion machine according to  claim 1 , wherein said active elements comprise at least one of the magnetocaloric materials selected in the group comprising gadolinium, a gadolinium alloy, an iron alloy, a manganese alloy, a lanthanum alloy, said alloys comprising at least one of the materials selected in the group comprising at least silicon, germanium, iron, magnesium, phosphorous, manganese, hydrogen, arsenic, or a combination of some of said materials. 
     
     
       13. A conversion machine according to  claim 12 , wherein the said magnetocaloric material has one of the forms selected from the group comprising a sheet, a porous block, a block of sheets, a pellet, powder, an agglomerate of pieces. 
     
     
       14. A conversion machine according to  claim 1 , wherein said magnetothermal converter has an annular configuration, said stator and said at least one rotor being superimposed radially and extending axially, wherein at least one part of fluidic passages provided in said active elements opens axially, and wherein fluidic connections are arranged in at least one axial end of said stator. 
     
     
       15. A conversion machine according to  claim 14 , wherein the said active elements are in the form of bars, extending axially into said stator, and each consisting of a block of porous material or of a block of sheets of material superposed and delimiting said fluidic passages between them. 
     
     
       16. A conversion machine according to  claim 1 , wherein the magnetic poles of said at least one rotor are obtained by a magnetic assembly selected from the group comprising one or more permanent magnets, ferrites, an electromagnet, a superconducting magnet, a superconducting electromagnet, a superconductor, a combination of these solutions, and wherein the non-magnetic poles of the said at least one rotor are obtained by the absence of magnetic assembly. 
     
     
       17. A conversion machine according to  claim 1 , further comprising several magnetothermal converters connected in series, in parallel, or in a series-parallel combination. 
     
     
       18. A conversion machine according to  claim 1 , wherein the said active elements comprise an assembly of several magnetocaloric materials of different Curie temperatures, organized in ascending or descending order. 
     
     
       19. A conversion machine according to  claim 1 , intended to convert electrical energy into thermal energy, further comprising an actuator coupled with said at least one rotor of said magnetothermal converter to expose said active elements to a variable magnetic field and alternately create in said active elements a magnetocaloric heating cycle and a magnetocaloric cooling cycle, wherein said fluidic circuit is coupled on the one hand with said stator to collect the thermal energy produced by said active elements, and on the other hand to an external device by means of at least one heat exchanger in order to transfer the thermal energy produced and simultaneously isolating said conversion machine from said at least one external device, wherein said magnetic modulation unit comprises said at least one rotor, and a synchronization system arranged to synchronize the circulation of the heat-transfer fluid from the fluidic circuit in the said active elements with the said magnetocaloric cycles. 
     
     
       20. A conversion machine according to  claim 1 , intended to convert thermal energy into electrical energy from a first thermal source at a first temperature and from a second thermal source at a second temperature different from the first temperature, further comprising an electromechanical converter coupled with said at least one rotor of said magnetothermal converter to convert mechanical energy into electrical energy, wherein said fluidic circuit is coupled on the one hand with said first thermal source by means of a first heat exchanger and to said second thermal source by means of a second heat exchanger to collect thermal energy and simultaneously isolating said conversion machine from said thermal sources, and is coupled on the other hand with said stator to transfer the thermal energy collected to said active elements, and wherein said thermal modulation unit comprises a synchronization system arranged to expose said active elements to temperature variations, generating a permanent magnetic imbalance between said at least one rotor and said stator, and producing the displacement of said at least one rotor to create said mechanical energy. 
     
     
       21. A conversion machine according to  claim 20 , wherein the said electromechanical converter is an electric generator, the rotor of said electric generator being coupled to said at least one rotor of said magnetothermal converter directly or by means of a speed reducer or multiplier to adapt the speeds of said rotors. 
     
     
       22. Use of a machine for converting thermal energy into electrical energy according to  claim 20  for recovering thermal energy from waste heat lost in a temperature range of −100° C. to +100° C. 
     
     
       23. Use of a conversion machine according to  claim 22 , wherein the temperature difference between the first thermal source and the second thermal source is at least equal to 10° C.